The Truth About Your Immune System

Can you boost immunity? Will vitamins, herbs, or probiotics help your immune system fight off disease? What about diet and exercise? The Truth about Your Immune System sets the record straight about how your immune system fights off germs and how you can help your immune system operate at its best.

The Truth About Your Immune System Cover

COVID-19, Flu, and Colds

Any given year, we’ll collectively come down with one billion colds and up to 45 million cases of flu, while the number of new cases of COVID-19 keeps rising. In this guide, you will learn how to avoid getting any of these three viral infections, and, if you do get sick, what you can do to feel better. You’ll also learn when your condition is serious enough to call a doctor. The report also provides specific information about high-risk…

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Can you boost immunity? Will vitamins, herbs, or probiotics help your immune system fight off disease? What about diet and exercise? Your immune system is your most powerful protector but don’t fall for claims that food products or vitamins will somehow support or improve your immunity. The Truth about Your Immune System sets the record straight about how your immune system fights off germs and how you can help your immune system operate at its best. This report includes practical steps you can take to improve your chances of staying healthy and to fight off infection from viruses, bacteria, fungus and other disease-causing microbes. Prepared in collaboration with the editors at Harvard Medical School and Michael N. Starnbach, Ph.D., professor of Microbiology and Molecular Genetics, Harvard Medical School. 38 pages. (2010)

Additional Resources

Animation: Herd Immunity
Vaccination protects individuals from disease, but it can also benefit an entire community by protecting even those few who are not vaccinated. The phenomenon is known as “herd immunity.” Here’s a simple demonstration that shows how it works … and how it can fail.


Video: The Immune System
In this interview, Michael Starnbach, PhD, replies to common questions about the immune system.



  • How your immune system works
    • When? Where? Why?
    • Microbes and hosts: Living together
    • The immune system in three acts
    • Act One: Defending the barricades
    • Act Two: Innate immunity
    • Act Three: Adaptive immunity
  • Special section: What about vaccines?
    • How vaccines work
    • Types of vaccines
    • Passive immunity
    • Do vaccines pose health risks?
    • Newer vaccine players
  • When things go wrong
    • Immunodeficiency disease
    • Hypersensitivity disorders (allergies)
    • Autoimmune disease
    • Trials and tribulations of transplantation
    • Cancer: Missed cues
  • What can you do?
    • Adopt healthy-living strategies
    • Beware the health claims on product labels
    • Age and immunity
    • Diet
    • Herbs and other supplements
    • Probiotics and prebiotics
    • The stress connection
    • Does being cold make you sick?
    • Exercise: Good or bad for immunity?
  • Looking ahead
  • Resources
  • Glossary

You can’t feel it or see it. You can’t take its pulse or its temperature. But out of sight and out of mind, your immune system is working to protect you from infectious bacteria, viruses, fungi, and parasites that cause disease, suffering, and death.

Despite its behind-the-scenes profile, the immune system is the subject of great attention in research laboratories like mine at Harvard Medical School. It is also a major target in the marketing departments of many businesses, as they try to sell their products based on the appealing but mistaken concept of boosting the immune system. At a time when we scientists are still trying to understand the basics of how the immune system works, product manufacturers have rushed to market everything from cereals to herbal teas that purport to support immunity with little evidence to back up those claims. Keep this in mind when you are tempted to pay extra for one of these products: consuming a food or supplement that contains vitamins, antioxidants, or other substances intended to support immunity delivers no additional benefit beyond that of taking an ordinary multivitamin pill.

If that sounds discouraging, you might be cheered to know that your immune system doesn’t need support beyond the ordinary measures you would take to stay healthy. Although not invincible, your immune response works exceedingly well. And even if it were possible to boost it into high gear, that wouldn’t necessarily be a good thing. A hyperactive immune response is the underlying problem causing diseases such as lupus, rheumatoid arthritis, diabetes, and multiple sclerosis. These conditions, known as autoimmune diseases, occur when the immune system, instead of attacking outside invaders, attacks the body’s own cells.

Powerful as it is, the immune response cannot fend off every germ that comes its way. In 2007, nearly 53,000 people in the United States died of influenza or pneumonia, making those diseases together the eighth leading cause of death. And nearly 35,000 died from sepsis, which results from severe bacterial infection. That’s more than the number who died from breast, colorectal, pancreatic, and prostate cancers combined. Worldwide, tuberculosis was responsible for 1.8 million deaths in 2007, and measles killed about 164,000 people in 2008, most of them children. At the same time, new infectious diseases are appearing around the globe in such forms as the H1N1 influenza that emerged in 2009 and the continuing threat of new bird flu strains.

The one truly powerful way to boost immunity is immunization. Most people alive today have enjoyed the health benefits of vaccination. Now, only the oldest generation remembers the dangers of life before vaccines. If you are lucky enough to know people over age 80, ask them what they remember of polio, diphtheria, whooping cough, and measles. Nearly all of them had relatives and neighbors who were crippled or killed by these diseases. As more parents decline to vaccinate their children, outbreaks of preventable diseases grow more common. Sadly, it is those children whose parents hoped to protect them by not vaccinating who will be most susceptible during an outbreak. This report is intended to fill the information gap with the truth about your immune system

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Thank you ever so much, Harvard Med School, for The Truth About Your Immune System. I finally got to grips with how the immune system works! And English is nowhere like my first language! The language here is uncomplicated, and easily understood. I only wish I had found it years ago! Brilliant pedagogics! Thanks again! Leif Akerlund, Sweden